<i>Background/Aims:</i> Patients with advanced Parkinson disease (PD) are at increased risk for asymptomatic leg deep venous thrombosis (DVT) because of severe motor fluctuations. Protracted immobility in the absence of antiparkinsonian therapy during stereotactic surgery may further increase the risk for venous thrombosis. Our aim was to determine the incidence of asymptomatic DVT of leg veins in PD patients undergoing subthalamic nucleus deep brain stimulation (STN-DBS). <i>Methods:</i> 41 consecutive PD patients undergoing stereotactic surgery for STN-DBS were investigated by ultrasound compression sonography of leg veins and D-dimer measurement in the week preceding surgery. After surgery, D-dimer measurements were repeated and when the value exceeded the normal range, ultrasound compression sonography was repeated to confirm or exclude DVT. <i>Results:</i> Doppler ultrasonographic examinations demonstrated that 2 patients (4.9%) developed asymptomatic DVT shortly after surgery (8.5 days) despite the fact that none of the 41 patients submitted to STN-DBS had DVT before surgery and that a specific prophylaxis was applied during surgery. <i>Conclusions:</i> Our data show that advanced PD patients are at risk for developing asymptomatic leg DVT following stereotactic surgery performed for STN-DBS. A strict clinical monitoring in the perioperative period is advisable in order to ensure early detection of DVT and prevent further thrombo-embolic complications.